The human body contains many joints that permit articulation of varying degrees between bones. Those that permit free articulation are referred to as diathroses. Examples include the hip, knee, elbow and shoulder. A variety of connective tissues are associated with the diathroses joints, including intra-articular cartilages that provide cushioning and smooth sliding surfaces, ligaments that provide flexible connections between bones and tendons that slide over joints and connect the muscles to provide motion. When connective tissues are compromised, joint pain and loss of function can result.
One example of compromised connective tissue is osteoarthritis of the knee or knee OA. Knee OA is one of the most common causes of disability in the United States. OA is sometimes referred to as degenerative, or wear and tear, arthritis. The knee joint is formed by the articulation of the femur, patella, and tibia (see FIG. 3). Like other freely articulating joints, the knee joint is enclosed by a fibrous joint capsule, lined by a synovial membrane. The inferior surface of the patella articulates with the femoral surface forming the patellofemoral joint. The distal end of the femur has two curved articular surfaces called the medial and lateral condyles. These surfaces articulate with the medial and lateral tibial condyles, forming the tibiofemoral joint, which flexes and extends the knee. Two fibrocartilagenous discs (i.e., menisci) lie between the tibial and femoral condyles to compensate for the incongruence of the articulating bones. Because the distal end of the femur is curved and asymmetric in shape, the knee joint not only flexes and extends like a hinge, but it also slides and rotates during flexion, resulting in a complex motion for the joint.
Knee OA is characterized by the breakdown of the articular cartilage within the joint. Over time, the cartilage may wear away entirely, resulting in bone-on-bone contact. Since bones, unlike cartilage, have many nerve cells, direct bone contact can be very painful to the OA sufferer. In addition to the pain and swelling, the OA sufferer can experience a progressive loss of mobility at the knee joint. This is due to loss of the joint space, where the articular cartilage has completely worn away. OA usually affects the side of the knee closest to the other knee (called the medial compartment) more often than the outside part (the lateral compartment). A bowlegged posture also places more pressure than normal on the medial compartment. The added pressure leads to more pain and faster degeneration where the cartilage is being squeezed together.
Various medications are often recommended to reduce the swelling and pain of OA. Other treatments such as weight loss, braces, orthotics, steroid injections, and physical therapy may also help alleviate pain and restore function. However, since articular cartilage is avascular, or lacks a blood supply, repair and growth of adult cartilage is minimal. If the pain or immobility becomes too severe and other therapies do not alleviate the symptoms, surgical interventions become necessary. In some cases, surgical treatment of OA may be appropriate. Surgeries can range from arthroscopic procedures to clean the joint by removing loose fragments of cartilage and by smoothening the rough spots on the cartilage to total knee replacement with an artificial knee.
Another surgical treatment for knee OA is proximal tibial osteotomy, a procedure intended to realign the angles in the lower leg to help shift pressure from the medial to the lateral side of the knee. The goal is to reduce the pain and delay further degeneration of the medial compartment.
In proximal tibial osteotomy, the upper (proximal) part of the tibia is cut, and the angle of the joint is changed. This converts the extremity from being bowlegged to straight or slightly knock-kneed. By correcting the joint deformity, pressure is taken off the cartilage. However, a proximal tibial osteotomy is only temporary before a total knee replacement becomes necessary. The benefits of the operation usually last for five to seven years if successful. The advantage to this approach is that very active people still have their own knee joint, and once the bone heals there are no restrictions on activities.
Another connective tissue disorder that occurs in the knee is excessive patellar compressive force (PCF). In patients suffering from patellofemoral arthritis, excessive compressive forces on the patella cause pain and lead to cartilage degeneration between the patella and femur.
Current treatments to relieve the excessive PCF in such patients involve highly invasive osteotomies to reposition the attachment point of the patellar tendon on the tibia. One such procedure is the Maquet procedure, which displaces the tibial tuberosity anteriorly by cutting away a portion of the bone and repositioning it with a bone graft inserted thereunder. Moving the attachment point of the patellar tendon anteriorly decreases the overall PCF by changing the moment arm and effective angle of the force. However, the procedure is highly invasive, involving high surgical morbidity and significant rehabilitation, which can be challenging for some patients. Lack of compliance with rehabilitation can also decrease positive outcomes even in initially successful procedures.
In addition to the Maquet osteotomy, there are other tibial tubercle procedures like the Fulkerson osteotomy and Elmslie-Trillat osteotomy that also displace the patellar tendon to reduce the compressive forces on the patella. The osteotomies also redistribute the load on the patella by transferring the load to other regions of the patella. These alternative procedures similarly involve relatively high surgical morbidity and require significant rehabilitation.
Another example of compromised connective tissue leading to joint pain and loss of function is hip dysplasia. The hip joint is the deepest and largest joint in the body, and is formed between the head of the femur and the acetabulum of the pelvis (see FIG. 27). The primary purpose of the hip joint is to support the weight of the body in both static (e.g., standing) and dynamic (e.g., running and walking) postures.
Hip dysplasia is a congenital or acquired deformation or a misalignment of the hip joint. The condition can range from barely detectable to severely malformed or dislocated. Early-age hip dysplasia can often be treated using a Pavlik harness or a Frejka pillow or splint. In older children, the hip abductor and iliopsoas muscles have to be treated surgically because they adapt to the dislocated joint position. Hip dysplasia is often cited as causing osteoarthritis (OA) of the hip at a comparatively young age. Dislocated load bearing surfaces lead to increased and unusual wear. Subsequent treatment with total hip arthroplasty (hip replacement) is complicated by a need for revision surgery due to skeletal changes as the body matures.
The current treatment for dysplasia-related pain is femoral neck osteotomy or periacetabular osteotomy. For more advanced cases, a total hip replacement is the only surgical option. In either case, the treatment involves extensive surgery with long rehabilitation protocols. There is thus a need for a less invasive, yet effective approach to treatment.
Compromise of connective tissues leading to joint pain and loss of function are not limited to humans. For example, the high frequency of canine hip dysplasia has made the canine hip a focus of attention among veterinary orthopedists. Canine hip dysplasia usually begins to manifest itself through decreased activity with varying degrees of joint pain. Often these signs are first observed between the ages of four months and one year.
In a normal canine hip joint, the head of the femur fits congruently into the acetabulum (see FIGS. 61A-B). In a dysplastic joint, the femoral head conforms poorly to the acetabulum. More space is evident between the bones. Displacement of the femoral head is the hallmark of the disease. As with human joint misalignment conditions, various surgical procedures—femoral head ostectomy, intertrochanteric osteotomy (ITO), triple pelvic osteotomy (TPO) and total hip replacement, have been devised to treat hip dysplasia. There is thus also a need for less invasive solutions to joint misalignment conditions and disease for canine and other veterinary applications.
Given the long-term ineffectiveness of current non-surgical treatments and the significant trauma of current surgical treatments, alternatives with significantly lower surgical morbidity and rehabilitation requirements could be beneficial to patients showing early as well as advanced symptoms of compromised connective tissue-related disorders of articular joints, such as hip dysplasia, and lateral knee and patellar femoral osteoarthritis.